The proposed research will examine factors that contribute to the initiation and maintenance of drug abuse in general, and opiate dependence in particular. The key concept for the present proposal concerns the interaction between environment (context), the organism, and the effects of opiates, and focuses on how conditioning and contextual cues affect the actions of drugs. The analysis makes use of the powerful tool of drug discrimination learning applied to a classical conditioning procedure (discriminated conditioned taste aversion), as well as to an operant procedure (discriminated two key responding). Specifically animals will be trained to detect morphine at different dose levels, followed by assessments of the discriminative stimulus effects as a function of drug- and contextual conditioning. The experimental designs to be used in this analysis include overshadowing, blocking, latent inhibition or pre- exposure effect, reversal learning, extinction, as well as random reinforcement training. These phenomena will be examined under varying contexts, involving different conditioning histories, and using the above designs which are aimed at the experimental analysis of such interactive effects. A particular emphasis is placed on the analysis of varying contextual cues during extinction. The studies are designed in order to provide an understanding of the complex interactions between a learning episode involving drug intake, and the accompanying contextual circumstances. Thus, a thorough examination of these complex interactions is necessary in order to fully understand and appreciate the complexity of drug actions and addiction.